Which of the following factors gives the elastin molecule the ability to stretch and recoil?
**Core Concept**
The elastin molecule, a crucial component of elastic fibers in connective tissue, exhibits unique elastic properties, allowing it to stretch and recoil. This ability is essential for maintaining tissue resilience and facilitating movements such as lung expansion and skin elasticity.
**Why the Correct Answer is Right**
Elastin molecules achieve their elastic properties due to their highly repetitive structure, rich in glycine and alanine residues. This structure allows the formation of a triple-helix conformation, enabling the molecule to extend and recoil by undergoing a series of coiled-coil transitions. The elastic recoil is facilitated by the hydrophobic interactions between the non-polar side chains of the amino acids, which drive the molecule to return to its original shape.
**Why Each Wrong Option is Incorrect**
**Option A:** Cross-linking between elastin molecules is essential for the stability and elasticity of elastic fibers. However, cross-linking alone does not give the elastin molecule its ability to stretch and recoil.
**Option B:** Collagen, another key protein in connective tissue, provides tensile strength but does not exhibit elastic properties like elastin.
**Option C:** Glycoproteins, such as fibronectin, play a role in cell adhesion and tissue organization, but they are not directly responsible for the elastic properties of elastin.
**Clinical Pearl / High-Yield Fact**
The elastin molecule's elastic properties are critical for maintaining tissue integrity and facilitating normal movements. Loss of elastin elasticity is associated with various age-related disorders, such as aortic aneurysms and skin laxity.
**Correct Answer: D. Hydrophobic interactions between non-polar side chains.**